A phone cord is 3.50 m long. The cord has a mass of 0.200 kg. A transverse wave pulse is produced by plucking one end of the taut cord. The pulse makes four trips down and back along the cord in 0.750 s. What is the tension in the cord?

 T = 1.24 N

Explanation:

The wave velocity is given by

        v = √T /μ

Wave speed is also

     v = λ f

Let's look for the wavelength that you rinse from an oscillation

    λ = 3.5 / 4 = 0.875 m

The frequency is the time of an oscillation

    f = 4 / t

    f = 4 / 0.75 = 5.33 s⁻¹

We equal the equation is

    λ f = √T /μ  

    T = λ²  f² μ  

Linear density is

    μ  = m / L

    μ  = 0.2 / 3.5

    μ  = 0.0571 kg / m

Let's calculate

   T = 0.875²  5.33²  0.0571

   T = 1.24 N

you'd use the equation that establishes a relationship between  energy  and  wavelength, which looks like this

e=h⋅cλ, where

λ  - the wavelength of the photon; c  - the speed of light, usually given as  3⋅108m/s; h  -  planck's constant, equal to  6.626⋅10−34j s

plug the value you were given for the energy of the photon in the above equation to get the wavelength

e=h⋅cλ⇒λ=h⋅ce

λ=6.626⋅10−34js⋅3⋅108ms−1.257⋅10−24j=1.581⋅10−1m